Interpretive Summary: Hammondia heydorni, a single celled parasite is very closely related to Neospora caninum and Toxoplasma gondii. Its diagnosis in a living animal is difficult. In the present paper authors report clinical illness in a dog and discuss differential diagnosis of these three closely related parasites. The results will be of interest to biologists, parasitologists, and veterinarians.

Technical Abstract:
A 10-year-old spayed female Italian Greyhound was presented to the Iowa State University College of Veterinary Medicine for evaluation of a two-month history of weight loss and anorexia with a two-week history of vomiting. The dog had recently received corticosteroid medication for suspected intervertebral disc disease. On physical examination, the dog was thin with a body condition score of 2.5/9 and had severe diffuse cachexia. Rectal examination revealed reddish-brown soft stool. Physical examination was otherwise unremarkable and no neurologic deficits were noted. Hematology revealed a mild anemia, mild neutrophilia and moderate thrombocytosis. Serum biochemistry revealed mild hypoalbuminemia and hypocalcemia. Urinalysis, thoracic radiographs and abdominal ultrasound revealed no abnormalities. Hammondia parasites were found in intestinal biopsy.